1. Field of the Invention
The present invention relates to a tracking system for tracking an electromagnetic energy source, for example, a communication satellite.
2. Description of the Prior Art
In a mobile telecommunication system wherein communication is performed between a telephone set installed in an automobile and a subscriber's station or another automobile through a stationary communication satellite or a repeater satellite. In the mobile telecommunication system, the automobile has an antenna which must be automatically controlled to track the satellite.
As a tracking system for tracking an electromagnetic energy source such as the satellite, a conical scanning system is known in the prior art where a beam of the antenna nutates or rotates in a cone shape while an electromagnetic wave from the satellite is received at the antenna as a receive signal. An angular error of the antenna beam from the satellite is detected as an error voltage from an amplitude modulation component in the receive signal. The antenna is moved until the error voltage becomes zero.
However, the conical scanning system has a disadvantage that the antenna has a complicated mechanism for rotating the antenna beam in a cone shape.
Another known tracking system is a step tracking system wherein the antenna is mechanically moved by a small angle in a direction to compare the receive signal strength before and after the move. A direction of the next move is decided according to the receive signal strength. Then, the antenna is again moved by the small angle in the decided direction. The similar operation is repeated until the maximum receive signal strength is obtained.
The step tracking system has a problem in a tracking speed. This is because the receive signal strength is decided after integrating the receive signal over a predetermined time period. Further, any compensator is necessary for compensating any displacement of the automobile with the antenna during the integrating time period.